Exactly. Although I've found it helpful to learn similar languages too (i.e. more than one scripting language). Seeing how subtle differences in the languages

Exactly. Although I've found it helpful to learn similar languages too (i.e. more than one scripting language). Seeing how subtle differences in the languages play out (beyond the superficial len/length type differences) has helped me understand some of the more subtle concepts of computer science. That said, you probably get the most bang-for-the-buck by picking up a language with a fundamentally different programming paradigm or at a lower or higher level than what you already know.